etcdserver: replace `forceVersionC` with `FirstCommitInTermNotify`

server/etcdserver/server.go

@@ -273,10 +273,6 @@ type EtcdServer struct {
 	peerRt   http.RoundTripper
 	reqIDGen *idutil.Generator
 
-	// forceVersionC is used to force the version monitor loop
-	// to detect the cluster version immediately.
-	forceVersionC chan struct{}
-
 	// wgMu blocks concurrent waitgroup mutation while server stopping
 	wgMu sync.RWMutex
 	// wg is used to wait for the goroutines that depends on the server state
@@ -528,7 +524,6 @@ func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
 		SyncTicker:         time.NewTicker(500 * time.Millisecond),
 		peerRt:             prt,
 		reqIDGen:           idutil.NewGenerator(uint16(id), time.Now()),
-		forceVersionC:      make(chan struct{}),
 		AccessController:   &AccessController{CORS: cfg.CORS, HostWhitelist: cfg.HostWhitelist},
 		consistIndex:       cindex.NewConsistentIndex(be.BatchTx()),
 		firstCommitInTermC: make(chan struct{}),
@@ -2084,10 +2079,6 @@ func (s *EtcdServer) applyEntryNormal(e *raftpb.Entry) {
 	if len(e.Data) == 0 {
 		s.notifyAboutFirstCommitInTerm()
 
-		select {
-		case s.forceVersionC <- struct{}{}:
-		default:
-		}
 		// promote lessor when the local member is leader and finished
 		// applying all entries from the last term.
 		if s.isLeader() {
@@ -2344,7 +2335,7 @@ func (s *EtcdServer) ClusterVersion() *semver.Version {
 func (s *EtcdServer) monitorVersions() {
 	for {
 		select {
-		case <-s.forceVersionC:
+		case <-s.FirstCommitInTermNotify():
 		case <-time.After(monitorVersionInterval):
 		case <-s.stopping:
 			return